Phase shift mask blank, phase shift mask, and blank preparing method

ABSTRACT

In a phase shift mask blank comprising a transparent substrate and a phase shift film deposited thereon and having a phase shift of 150-200° with respect to sub-200 nm light, the phase shift film is composed of a silicon base material consisting of silicon, nitrogen and optionally oxygen, has a thickness of up to 70 nm, and provides a warpage change of up to 0.2 μm in a central region of a surface of the substrate before and after the deposition of the phase shift film on the substrate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of co-pending application Ser. No.15/077,296 filed on Mar. 22, 2016, which claims priority under 35 U.S.C.§ 119(a) to Patent Application No. 2015-072766 filed in Japan on Mar.31, 2015, all of which are hereby expressly incorporated by referenceinto the present application.

TECHNICAL FIELD

This invention relates to a phase shift mask for use in themicrofabrication of semiconductor integrated circuits or the like, aphase shift mask blank, and a method for preparing the mask blank.

BACKGROUND ART

In the field of semiconductor technology, research and developmentefforts are continued for further miniaturization of pattern features.Recently, as advances including miniaturization of circuit patterns,thinning of interconnect patterns and miniaturization of contact holepatterns for connection between cell-constituting layers are in progressto comply with higher integration density of LSIs, there is anincreasing demand for the micropatterning technology. Accordingly, inconjunction with the technology for manufacturing photomasks used in theexposure step of the photolithographic microfabrication process, it isdesired to have a technique of forming a more fine and accurate circuitpattern or mask pattern.

In general, reduction projection is employed when patterns are formed onsemiconductor substrates by photolithography. Thus the size of patternfeatures formed on a photomask is about 4 times the size of patternfeatures formed on a semiconductor substrate. In the currentphotolithography technology, the size of circuit patterns printed issignificantly smaller than the wavelength of light used for exposure.Therefore, if a photomask pattern is formed simply by multiplying thesize of circuit pattern 4 times, the desired pattern is not transferredto a resist film on a semiconductor substrate due to opticalinterference and other effects during exposure.

Sometimes, optical interference and other effects during exposure aremitigated by forming the pattern on a photomask to a more complex shapethan the actual circuit pattern. Such a complex pattern shape may bedesigned, for example, by incorporating optical proximity correction(OPC) into the actual circuit pattern. Also, attempts are made to applythe resolution enhancement technology (RET) such as modifiedillumination, immersion lithography or double exposure (or doublepatterning) lithography, to meet the demand for miniaturization andhigher accuracy of patterns. The phase shift method is used as one ofthe RET. The phase shift method is by forming a pattern of film capableof phase reversal of approximately 180 degrees on a photomask, such thatcontrast may be improved by utilizing optical interference. One of thephotomasks adapted for the phase shift method is a halftone phase shiftmask. Typically, the halftone phase shift mask includes a substrate ofquartz or similar material which is transparent to exposure light, and amask pattern of halftone phase shift film formed on the substrate,capable of providing a phase shift of approximately 180 degrees andhaving an insufficient transmittance to contribute to pattern formation.As the halftone phase shift mask, Patent Document 1 (JP-A H07-140635)proposes a mask having a halftone phase shift film of molybdenumsilicide oxide (MoSiO) or molybdenum silicide oxynitride (MoSiON).

For the purpose of forming finer images by photolithography, light ofshorter wavelength is used as the light source. In the currently mostadvanced stage of lithography process, the exposure light source hasmade a transition from KrF excimer laser (248 nm) to ArF excimer laser(193 nm). The lithography using ArF excimer laser light of greaterenergy was found to cause damages to the mask, which were not observedwith KrF excimer laser light. One problem is that on continuous use ofthe photomask, foreign matter-like growth defects form on the photomask.These growth defects are also known as “haze”. The source of hazeformation was formerly believed to reside in the growth of ammoniumsulfate crystals on the mask pattern surface. It is currently believedthat organic matter participates in haze formation as well.

Some approaches are known to overcome the haze problem. With respect tothe growth defects formed on the photomask upon long-term irradiation ofArF excimer laser light, for example, Patent Document 2 (JP-A2008-276002) describes that if the photomask is cleaned at apredetermined stage, then it can be continuously used.

As the exposure dose of ArF excimer laser light irradiated for patterntransfer increases, the photomask is given damage different from haze;and the size of the mask pattern changes in accordance with thecumulative irradiation energy dose, as reported in Non-Patent Document 1(Thomas Faure et al., “Characterization of binary and attenuated phaseshift mask blanks for 32 nm mask fabrication,” Proc. of SPIE, vol. 7122,pp 712209-1 to 712209-12). This problem is that as the cumulativeirradiation energy dose increases during long-term irradiation of ArFexcimer laser light, a layer of a substance which is considered to be anoxide of the pattern material grows outside the film pattern, wherebythe pattern width changes. It is also reported that the mask oncedamaged cannot be restored by cleaning with AMP (aqueousammonia/hydrogen peroxide) as used in the above-mentioned haze removalor with SPM (sulfuric acid/hydrogen peroxide). It is believed that thedamage source is utterly different.

Non-Patent Document 1 points out that upon exposure of a circuit patternthrough a halftone phase shift mask which is the mask technology usefulin expanding the depth of focus, substantial degradation is induced bypattern size variation resulting from alteration of a transitionmetal/silicon base material film such as MoSi base material film byirradiation of ArF excimer laser light (this degradation is referred toas “pattern size variation degradation”). Then, in order to use anexpensive photomask over a long period of time, it is necessary toaddress the pattern size variation degradation by irradiation of ArFexcimer laser light.

As pointed out in Non-Patent Document 1, the pattern size variationdegradation by irradiation of short wavelength light, typically ArFexcimer laser light does scarcely occur when light is irradiated in adry air atmosphere. Exposure in a dry air atmosphere is regarded as anew approach for inhibiting the pattern size variation degradation.However, the control of a dry air atmosphere adds an extra unit to theexposure system and gives rise to electrostatic and other problems to bemanaged, leading to an increased expense. Under the circumstances, it isnecessary to enable long-term exposure in a common atmosphere that doesnot need complete removal of humidity (typically having a humidity ofaround 50%).

The photomasks used in the lithography using ArF excimer laser light aslight source include halftone phase shift masks having a halftone phaseshift film of a silicon base material containing a transition metal,typically molybdenum. This silicon base material is mainly composed of atransition metal and silicon, and further contains oxygen and/ornitrogen as light element (e.g., Patent Document 1). Suitable transitionmetals used include Mo, Zr, Ta, W, and Ti. Among others, Mo is mostoften used (e.g., Patent Document 1). Sometimes a second transitionmetal is added (e.g., Patent Document 3). For the light-shielding film,silicon base materials containing a transition metal, typicallymolybdenum are also used. However, when a photomask using suchtransition metal-containing silicon base material is exposed to a largedose of high-energy radiation, the mask undergoes significant patternsize variation degradation by irradiation of high-energy radiation. Thenthe service lifetime of the photomask is shorter than the requirement.

It is a serious problem that when a photomask pattern on a halftonephase shift mask is irradiated with short-wavelength light, typicallyArF excimer laser light, the photomask pattern for exposure experiencesa variation of line width, that is, “pattern size variationdegradation.” The permissible threshold of pattern width differs withthe type of photomask pattern, especially the pattern rule appliedthereto. If variations are small, the mask may be further used bycorrecting the exposure conditions and resetting the irradiationconditions of an exposure system. For example, in the lithography forforming semiconductor circuits complying with the pattern rule of 22 nm,the variation of mask pattern line width must fall within approximately±5 nm. However, if a pattern width variation is large, there is apossibility that the variation has an in-plane distribution on thephotomask. Also in the further miniaturization technology, an auxiliarypattern having an ultrafine size of less than 100 nm is formed on themask. For the purpose of pattern miniaturization on these masks and fromthe aspect of an increase of mask processing cost by complication ofmask pattern, there is a need for a halftone phase shift mask film whichexperiences minimal pattern size variation degradation and allows forrepeated exposure.

On use of a halftone phase shift mask blank in the halftone phase shiftmask producing process, if foreign deposits are on the mask blank, theycause defects to the pattern. To remove foreign deposits, the halftonephase shift mask blank is cleaned many times during the mask producingprocess. Further, when the halftone phase shift mask thus produced isused in the photolithography process, the mask is also repeatedlycleaned even if the mask itself is free of pattern defects, for thereason that if foreign deposits settle on the mask during thephotolithography process, a semiconductor substrate which is patternedusing that mask eventually bears pattern-transfer failures.

For removing foreign deposits from the halftone phase shift mask blankor mask, chemical cleaning is applied in most cases, using SPM, ozonewater or AMP. SPM is a sulfuric acid/hydrogen peroxide mixture which isa cleaning agent having strong oxidizing action. Ozone water is waterhaving ozone dissolved therein and used as a replacement of SPM. AMP isan aqueous ammonia/hydrogen peroxide mixture. When the mask blank ormask having organic foreign deposits on its surface is immersed in theAMP cleaning liquid, the organic foreign deposits are liberated andremoved from the surface under the dissolving action of ammonia and theoxidizing action of hydrogen peroxide.

Although the chemical cleaning with such chemical liquid is necessaryfor removing foreign deposits such as particles and contaminants on thehalftone phase shift mask blank or mask, the chemical cleaning candamage the halftone phase shift film on the mask blank or mask. Forexample, if the surface of a halftone phase shift film is altered bychemical cleaning, the optical properties that the film originallypossesses can be changed. In addition, chemical cleaning of the halftonephase shift mask blank or mask is repeatedly carried out. It is thusnecessary to minimize any property change (e.g., phase shift change) ofthe halftone phase shift film during every cleaning step.

CITATION LIST

-   -   Patent Document 1: JP-A H07-140635    -   Patent Document 2: JP-A 2008-276002 (U.S. Pat. No. 7,941,767)    -   Patent Document 3: JP-A 2004-133029    -   Patent Document 4: JP-A 2007-033469    -   Patent Document 5: JP-A 2007-233179    -   Patent Document 6: JP-A 2007-241065    -   Non-Patent Document 1: Thomas Faure et al., “Characterization of        binary and attenuated phase shift mask blanks for 32 nm mask        fabrication,” Proc. of SPIE, vol. 7122, pp 712209-1 to 712209-12

SUMMARY OF INVENTION

With respect to the phase shift film, a thinner film is advantageous forpattern formation and effective for reducing 3D effect. Thus a thinnerfilm is required in order for photolithography to form a finer sizepattern.

As alluded to previously (Patent Document 1), a film containingmolybdenum and silicon is mainly used as the phase shift film.Regrettably, the transition metal-containing film experiences anoticeable pattern size variation degradation by irradiation of ArFexcimer laser light of wavelength 193 nm. Since cleaning is repeatedduring the mask manufacture process or mask use, the transitionmetal-containing film also undergoes noticeable changes of opticalproperties on every cleaning. These problems may be solved by formingthe phase shift film from a transition metal-free silicon base material.Nevertheless, the phase shift film formed of a transition metal-freesilicon base material, especially nitrogen-containing silicon basematerial contains a substantial stress therein. When a phase shift maskis manufactured from this phase shift mask blank by patterning the phaseshift film, a flatness change occurs before and after the patternformation of the phase shift film, resulting in misalignment of thepattern on the phase shift mask, that is, a low dimensional accuracy.

An object of the invention is to provide a phase shift mask blank havinga phase shift film which is thin enough to be advantageous for patternformation and 3D effect reduction while maintaining a necessary phaseshift for the phase shift function to comply with pattern sizeminiaturization, and is improved in quality and dimensional control soas to minimize pattern misalignment and dimensional accuracy loweringduring the step of patterning the phase shift film to form a phase shiftmask. Another object is to provide a phase shift mask and a method forpreparing the phase shift mask blank.

Aiming to develop a phase shift film which has a reduced thickness andis minimized in pattern misalignment and dimensional accuracy loweringduring the step of patterning the phase shift film to form a phase shiftmask while maintaining a necessary phase shift for the phase shiftfunction, the inventors made a study on a transition metal-free phaseshift film. It has been found that a desired phase shift film is formedon a transparent substrate by sputter depositing at least one layer of asilicon base material consisting of silicon, nitrogen and optionallyoxygen and heat treating the film at 400° C. or above for at least 5minutes. Then the phase shift film has a thickness of up to 70 nm and aphase shift of 150 to 200° with respect to light of wavelength up to 200nm light and provides a warpage change (ΔTIR) of up to 0.2 μm asabsolute value in a central region of 142 mm squares on a surface of thesubstrate between before the deposition of the phase shift film on thesubstrate and the presence of the phase shift film on the substrate, ora warpage change (ΔTIR) of up to 0.2 μm as absolute value in a centralregion of 142 mm squares on a surface of the substrate between thepresence of the phase shift film on the substrate and after completeremoval of the phase shift film from the substrate by etching.

Once the phase shift film is constructed as above, there is obtained aphase shift mask blank which can be advantageously processed into aphase shift film pattern including a main photomask pattern with a widthof about 100 to 200 nm, which is necessary in photolithography forforming a pattern with a half pitch of up to 50 nm on a processablesubstrate such as silicon wafer, using exposure light of wavelength upto 200 nm. The phase shift film is minimized in pattern misalignment andimproved in dimensional accuracy during the step of patterning the phaseshift film.

Accordingly, in one aspect, the invention provides a phase shift maskblank comprising a transparent substrate of 152 mm squares and 6.35 mmthick and a phase shift film deposited on the substrate and having aphase shift of 150 to 200° with respect to light of wavelength up to 200nm. The phase shift film includes at least one layer composed of asilicon base material consisting of silicon and nitrogen or a siliconbase material consisting of silicon, nitrogen and oxygen, has athickness of up to 70 nm, and provides a warpage change (ΔTIR) of up to0.2 μm as absolute value in a central region of 142 mm squares on asurface of the substrate between before the deposition of the phaseshift film on the substrate and the presence of the phase shift film onthe substrate.

In another aspect, the invention provides a phase shift mask blankcomprising a transparent substrate of 152 mm squares and 6.35 mm thickand a phase shift film deposited on the substrate and having a phaseshift of 150 to 200° with respect to light of wavelength up to 200 nm.The phase shift film includes at least one layer composed of a siliconbase material consisting of silicon and nitrogen or a silicon basematerial consisting of silicon, nitrogen and oxygen, has a thickness ofup to 70 nm, and provides a warpage change (ΔTIR) of up to 0.2 μm asabsolute value in a central region of 142 mm squares on a surface of thesubstrate between the presence of the phase shift film on the substrateand after complete removal of the phase shift film from the substrate byetching.

In a preferred embodiment, the phase shift film is a halftone phaseshift film composed of a silicon base material consisting of silicon andnitrogen and having a transmittance of 3% to less than 20% with respectto light of wavelength up to 200 nm.

In another preferred embodiment, the phase shift film is a halftonephase shift film composed of a silicon base material consisting ofsilicon, nitrogen and oxygen and having a transmittance of at least 20%with respect to light of wavelength up to 200 nm.

The mask blank may further comprise a second film on the phase shiftfilm, the second film being a single layer or a multilayer film composedof a chromium-containing material. Typically, the second film is alight-shielding film, a combination of light-shielding film andantireflective film, or an auxiliary film which functions as a hard maskduring pattern formation of the phase shift film.

The mask blank may further comprise a third film on the second film, thethird film being a single layer or a multilayer film composed of asilicon-containing material. In a preferred embodiment, the second filmis a light-shielding film or a combination of light-shielding film andantireflective film, and the third film is an auxiliary film whichfunctions as a hard mask during pattern formation of the second film. Inanother preferred embodiment, the second film is an auxiliary film whichfunctions as a hard mask during pattern formation of the phase shiftfilm and as an etch stopper during pattern formation of the third film,and the third film is a light-shielding film or a combination oflight-shielding film and antireflective film.

The mask blank may further comprise a fourth film on the third film, thefourth film being a single layer or a multilayer film composed of achromium-containing material. In a preferred embodiment, the second filmis an auxiliary film which functions as a hard mask during patternformation of the phase shift film and as an etch stopper during patternformation of the third film, the third film is a light-shielding film ora combination of light-shielding film and antireflective film, and thefourth film is an auxiliary film which functions as a hard mask duringpattern formation of the third film.

In any embodiments, the phase shift film has been sputter deposited andheat treated at 400° C. or above for at least 5 minutes.

Also contemplated herein is a phase shift mask prepared from the phaseshift mask blank defined above.

In a further aspect, the invention provides a method for preparing aphase shift mask blank comprising the steps of sputter depositing aphase shift film on a transparent substrate, and heat treating the phaseshift film on the substrate at 400° C. or above for at least 5 minutes.The depositing step includes one or both of step (A) of depositing alayer composed of a silicon base material consisting of silicon andnitrogen on a transparent substrate by using a sputtering system with achamber and at least one silicon target, and feeding argon gas andnitrogen gas into the chamber, and step (B) of depositing a layercomposed of a silicon base material consisting of silicon, nitrogen andoxygen on a transparent substrate by using a sputtering system with achamber and at least one silicon target, and feeding argon gas, and atleast one gas selected from nitrogen gas, oxygen gas and nitrogen oxidegas into the chamber.

Advantageous Effects of Invention

The phase shift mask blank of the invention has a phase shift film whichis thin enough to be advantageous for photomask pattern formation,improved in quality and dimensional control so as to minimize patternmisalignment and dimensional accuracy lowering during the step ofpatterning the phase shift film to manufacture a phase shift mask, andmaintains a necessary phase shift for the phase shift function. Usingthe phase shift mask, lithography exposure complying with therequirements of pattern miniaturization and patterning accuracy becomespossible.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B are cross-sectional views of one exemplary phase shiftmask blank and phase shift mask of the invention, respectively.

FIGS. 2A, 2B and 2C are cross-sectional views of further embodiments ofthe phase shift mask blank of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

The invention pertains to a phase shift (photo)mask blank comprising atransparent substrate and a phase shift film formed thereon. Thetransparent substrate is typically a quartz substrate. Preference isgiven to transparent substrates of 6 inch squares and 25 mil thick,known as 6025 substrate, as prescribed in the SEMI standards, ortransparent substrates of 152 mm squares and 6.35 mm thick whenexpressed in the SI units. The phase shift film may be a single layerstructure or a multilayer structure (i.e., two or more layers). Thephase shift (photo)mask has a (photo)mask pattern of a phase shift film.The term “phase shift film” is inclusive of a halftone phase shift film.Accordingly, the phase shift mask blank is inclusive of a halftone phaseshift mask blank, and the phase shift mask is inclusive of a halftonephase shift mask.

FIG. 1A is a cross-sectional view of a phase shift mask blank in oneembodiment of the invention. The phase shift mask blank 100 includes atransparent substrate 10 and a phase shift film 1 formed thereon. FIG.1B is a cross-sectional view of a phase shift mask in one embodiment ofthe invention. The phase shift mask 101 includes a transparent substrate10 and a phase shift film pattern 11 thereon.

The phase shift film may be composed of a single layer Or multiplelayers as long as a phase shift and a transmittance necessary for thephase shift function are met. In the case of multilayer structure, thefilm is preferably composed of multiple layers including anantireflective function layer so that the overall film may meet apredetermined surface reflectance as well as the necessary phase shiftand transmittance.

In either of the single layer and multilayer structure, each layer maybe a uniform layer or a compositionally graded layer (i.e., a layerwhose composition varies continuously in thickness direction). In thecase of multilayer structure, the phase shift film may be a combinationof two or more layers selected from layers composed of differentconstituents and layers composed of identical constituents in differentcompositional ratios. Where the film is composed of three or morelayers, identical layers may be included as long as they are notcontiguous to each other.

Since phase shift masks are used in the photolithography using exposurelight of wavelength up to 200 nm, typically ArF excimer laser light(wavelength 193 nm), the phase shift film should provide a predeterminedphase shift and a predetermined transmittance with respect to theexposure light at a predetermined thickness.

The (overall) thickness of the phase shift film should preferably be upto 70 nm, and more preferably up to 62 nm, because a thinner filmfacilitates to form a finer pattern. The lower limit of the filmthickness is set in the range where the desired optical properties areobtained relative to light of wavelength up to 200 nm. Specifically, thefilm thickness is set at least 40 nm, though the lower limit is notcritical.

The phase shift of the phase shift film with respect to exposure lightis such that a phase shift between the exposure light transmitted by aregion of phase shift film (phase shift region) and the exposure lighttransmitted by a neighboring region where the phase shift film isremoved, causes interference of exposure light at the boundary wherebycontrast is increased. Specifically the phase shift is 150 to 200degrees. Although ordinary phase shift films are set to a phase shift ofapproximately 180°, it is possible from the standpoint of contrastenhancement to adjust the phase shift below or beyond 180°. For example,setting a phase shift of smaller than 180° is effective for forming athinner film. It is a matter of course that a phase shift closer to 180°is more effective because a higher contrast is available. In thisregard, the phase shift is preferably 160 to 190°, more preferably 175to 185°, and most preferably approximately 180°.

In one embodiment, the phase shift film provides a warpage change (ΔTIR)of up to 0.2 μm as absolute value in a central region of 142 mm squareson a surface of the substrate before and after the deposition of thephase shift film on the substrate, i.e., between the absence and thepresence of the phase shift film. In another embodiment, the phase shiftfilm provides a warpage change (ΔTIR) of up to 0.2 μm as absolute valuein a central region of 142 mm squares on a surface of the substratebetween the presence of the phase shift film on the substrate and aftercomplete removal of the phase shift film from the substrate by etching.Now that the phase shift film is designed so as to minimize a warpagechange, there is obtained a phase shift mask blank having a phase shiftfilm which is minimized in pattern misalignment and dimensional accuracylowering during the step of patterning the phase shift film to form aphase shift mask.

The central region of 142 mm squares on the surface of a transparentsubstrate is defined as a range that extends inward from a positionspaced 5 mm apart from each side of the surface of a transparentsubstrate of 152 mm squares on which a phase shift film is deposited.This range corresponds to a region of a phase shift mask where aphotomask pattern used for exposure is formed. The warpage (or sori) ofthe bare transparent substrate and the phase shift film-bearingtransparent substrate is a flatness as prescribed by TIR (totalindicator reading) on measurement of the surface topography of thesubstrate by surface topography analyzing system or flatness tester.When the surface topography of an identical substrate is measured on theassumption that the height at the center of the substrate is an originin height direction, a warpage change (ΔTIR) is defined as the maximumor minimum of a change at each coordinate in the substrate surface(plane) between the presence and the absence of the film on thesubstrate. The warpage and warpage change may be measured and computedby a commercial flatness tester, for example, Tropel® UltraFlat 200 Mask(Corning Inc.).

In the embodiment wherein the phase shift film is a halftone phase shiftfilm, the phase shift film has a transmittance of exposure light whichis preferably at least 3%, more preferably at least 5%, and up to 40%,more preferably up to 30%.

Particularly when the phase shift film is composed of a silicon basematerial consisting of silicon and nitrogen, it may be formed as ahalftone phase shift film having a transmittance of 3% to less than 20%with respect to sub-200 nm wavelength light by adjusting the contents ofsilicon and nitrogen in the film. Also when the phase shift film iscomposed of a silicon base material consisting of silicon, nitrogen andoxygen, it may be formed as a halftone phase shift film having atransmittance of at least 20% with respect to sub-200 nm wavelengthlight by adjusting the contents of silicon, nitrogen and oxygen in thefilm.

When the phase shift film is a single layer, the overall single layer,or when the film is a multilayer film, at least one layer, especiallythe overall layers (excluding a surface oxidized layer if any) shouldpreferably have a refractive index n of at least 2.4, more preferably atleast 2.5, and even more preferably at least 2.6 with respect to theexposure light. By reducing the oxygen content of a phase shift film,preferably by eliminating oxygen, or by eliminating transition metalfrom the film, the refractive index n of the film can be increased whilemaintaining the predetermined transmittance, and the thickness of thefilm can be reduced while maintaining the necessary phase shift for thephase shift function. The refractive index n becomes higher as theoxygen content is lower, and the necessary phase shift is available froma thinner film as the refractive index n is higher.

When the phase shift film is a single layer, the overall single layer,or when the film is a multilayer film, at least one layer, especiallythe overall layers (excluding a surface oxidized layer if any) shouldpreferably have an extinction coefficient k of at least 0.1, especiallyat least 0.2 and up to 0.7, especially up to 0.65.

The phase shift film includes at least one layer composed of a siliconbase material consisting of silicon and nitrogen or a silicon basematerial consisting of silicon, nitrogen and oxygen. The silicon basematerial contains silicon and nitrogen and optionally oxygen. Elementsother than these are permissible as long as their amount is at animpurity level. Preferably, transition metals such as molybdenum,zirconium, tungsten, titanium, hafnium, chromium and tantalum are notcontained. Use of such silicon base material overcomes the pattern sizevariation degradation problem associated with transitionmetal-containing silicon base materials. Also use of such silicon basematerial provides for improved chemical resistance against chemicalcleaning.

In the embodiment wherein the phase shift film is a multilayer film, thethickness of a layer composed of a silicon base material consisting ofsilicon and nitrogen or a silicon base material consisting of silicon,nitrogen and oxygen is preferably at least 60%, more preferably at least80% of the total thickness of the phase shift film. If two or more suchlayers are included, the total thickness of these layers is preferablyat least 60%, more preferably at least 80% of the total thickness of thephase shift film. Where a surface oxidized layer is included as will bedescribed later, preferably all the layers of the film excluding thesurface oxidized layer are layers composed of a silicon base materialconsisting of silicon and nitrogen or a silicon base material consistingof silicon, nitrogen and oxygen. Also in the embodiment wherein thehalftone phase shift film is a multilayer film, the layer composed of asilicon base material consisting of silicon and nitrogen or a siliconbase material consisting of silicon, nitrogen and oxygen may be disposedat any level in the film selected from the side adjacent to thesubstrate, the side remote from the substrate, and the center inthickness direction.

When the phase shift film is a single layer, the silicon base materialof the overall single layer, or when the film is a multilayer film, thesilicon base material of at least one layer, especially all the layers(excluding a surface oxidized layer if any) should preferably have asilicon content of at least 30 at %, more preferably at least 40 at %,even more preferably at least 44 at %, and up to 55 at %, morepreferably up to 50 at %. In particular, when the phase shift film is ahalftone phase shift film having a low transmittance of specificallyfrom 3% to less than 20%, more specifically from 3% to 12%, and evenmore specifically from 3% to less than 10%, the silicon base materialpreferably has a silicon content of at least 40 at %, more preferably atleast 44 at %, and up to 55 at %, and more preferably up to 50 at %.When the phase shift film is a halftone phase shift film having a hightransmittance of specifically from 20% to 30%, the silicon base materialpreferably has a silicon content of at least 30 at %, more preferably atleast 40 at %, and up to 55 at %, and more preferably up to 45 at %.

When the phase shift film is a single layer, the silicon base materialof the overall single layer, or when the film is a multilayer film, thesilicon base material of at least one layer, especially all the layers(excluding a surface oxidized layer if any) should preferably have anitrogen content of at least 10 at %, more preferably at least 40 at %,and up to 60 at %, more preferably up to 55 at %. In particular, whenthe phase shift film is a halftone phase shift film having a lowtransmittance of specifically from 3% to less than 20%, morespecifically from 3% to 12%, and even more specifically from 3% to lessthan 10%, the silicon base material preferably has a nitrogen content ofat least 44 at %, and up to 60 at %, and more preferably up to 56 at %.When the phase shift film is a halftone phase shift film having a hightransmittance of specifically from 20% to 30%, the silicon base materialpreferably has a nitrogen content of at least 10 at %, more preferablyat least 40 at %, and up to 60 at %, more preferably up to 55 at %.

When the phase shift film is a single layer, the silicon base materialof the overall single layer, or when the film is a multilayer film, thesilicon base material of at least one layer, especially all the layers(excluding a surface oxidized layer if any) should preferably have anoxygen content of up to 50 at %, more preferably up to 20 at %, and evenmore preferably up to 6 at %. In particular, when the phase shift filmis a halftone phase shift film having a low transmittance ofspecifically from 3% to less than 20%, more specifically from 3% to 12%,and even more specifically from 3% to less than 10%, the silicon basematerial preferably has an oxygen content of at least 0 at %, and up to6 at %, more preferably up to 3.5 at %, and even more preferably up to 1at %. When the phase shift film is a halftone phase shift film having ahigh transmittance of specifically from 20% to 30%, the silicon basematerial preferably has an oxygen content of up to 50 at %, morepreferably up to 20 at %, and in particular, the phase shift film shouldpreferably include at least one layer of a silicon base material havingan oxygen content of at least 0 at %, more preferably at least 1 at %.

Suitable silicon base materials include a silicon base materialconsisting of silicon and nitrogen, i.e., silicon nitride (SiN) and asilicon base material consisting of silicon, nitrogen and oxygen, i.e.,silicon oxynitride (SiON).

In order to form a phase shift film as a thin film, a silicon basematerial with a lower oxygen content is preferred, with an oxygen-freematerial being more preferred. From this aspect, the phase shift filmshould preferably include a layer composed of a silicon base materialconsisting of silicon and nitrogen. In this context, the phase shiftfilm is advantageously a single layer composed of a silicon basematerial consisting of silicon and nitrogen, or a multilayer filmincluding at least one layer composed of a silicon base materialconsisting of silicon and nitrogen, especially including at least onelayer composed of a silicon base material consisting of silicon andnitrogen and at least one layer composed of a silicon base materialconsisting of silicon, nitrogen and oxygen.

While the phase shift film may be deposited by any well-knownfilm-forming techniques, the sputtering technique is preferred becausefilms of homogeneity are readily deposited. Either DC sputtering or RFsputtering may be employed. The target and sputtering gas may beselected as appropriate depending on the layer construction andcomposition of the film. Suitable targets include a silicon target, asilicon nitride target, and a target containing silicon and siliconnitride. The contents of nitrogen and oxygen may be adjusted duringreactive sputtering by using nitrogen-containing gas, oxygen-containinggas, or nitrogen/oxygen-containing gas, and optionally carbon-containinggas, as the reactive gas, and adjusting the flow rate thereof. Thereactive gas is, for example, nitrogen gas (N₂ gas), oxygen gas (O₂gas), nitrogen oxide gases (N₂O gas, NO gas, NO₂ gas). It isadvantageous from the aspect of reducing a warpage change (ΔTIR) to usea rare gas such as helium, neon or argon gas in the sputtering gas.

According to the invention, a phase shift mask blank as defined above ispreferably prepared by sputter depositing a phase shift film on atransparent substrate such that the film may include at least one layerof a silicon base material consisting of silicon, nitrogen andoptionally oxygen, and heat treating the phase shift film on thesubstrate at a temperature of at least 400° C. for at least 5 minutes.

Preferably the step of sputter depositing a phase shift film on atransparent substrate includes one or both of step (A) of depositing alayer composed of a silicon base material consisting of silicon andnitrogen on a transparent substrate by using a sputtering system with achamber and at least a silicon target, and feeding argon gas andnitrogen gas into the chamber, and step (B) of depositing a layercomposed of a silicon base material consisting of silicon, nitrogen andoxygen on a transparent substrate by using a sputtering system with achamber and at least a silicon target, and feeding argon gas, and atleast one gas selected from nitrogen gas, oxygen gas and nitrogen oxidegas into the chamber. In the step of sputter depositing a phase shiftfilm, the flow rate of sputtering gas is preferably adjusted such thatthe resulting phase shift film may cause a minimal warpage change (ΔTIR)in the phase shift mask blank.

The heat treatment of the phase shift film following deposition ispreferably by heating the phase shift film deposited on the substrate ata temperature of at least 400° C., especially at least 450° C. for atime of at least 5 minutes, especially at least 30 minutes. If atransition metal-containing film used as the phase shift film in theprior art is heat treated at such high temperature, precipitates form onthe surface and become defects. High temperature is not applicable tothe prior art film. In contrast, a phase shift film including at leastone layer of a silicon base material consisting of silicon, nitrogen andoptionally oxygen does not give rise to the problem associated with thetransition metal-containing film, even when such high temperature isapplied. The heat treatment temperature is preferably up to 900° C.,more preferably up to 700° C. and the time is preferably up to 24 hours,more preferably up to 12 hours. Heat treatment may be performed withinthe sputtering chamber or after transfer of the substrate to a heattreating furnace apart from the sputtering chamber. The heat treatmentatmosphere may be an inert gas atmosphere such as helium gas or argongas or vacuum. Also an oxygen-containing atmosphere such as oxygen gasatmosphere may be used although a surface oxidized layer is formed onthe outermost surface.

In the embodiment wherein the phase shift film is a multilayer film, thefilm may include a surface oxidized layer as the outermost layer on thesurface side (disposed remote from the substrate) in order to suppressany change in quality of the film. The surface oxidized layer may havean oxygen content of at least 20 at %, with even an oxygen content of atleast 50 at % being acceptable. The surface oxidized layer may be formedby atmospheric or air oxidation or forced oxidative treatment. Examplesof forced oxidative treatment include treatment of a silicon-basedmaterial film with ozone gas or ozone water, and heating of a film at300° C. or higher in an oxygen-containing atmosphere, typically oxygengas atmosphere by oven heating, lamp annealing or laser heating. Thesurface oxidized layer preferably has a thickness of up to 10 nm, morepreferably up to 5 nm, and even more preferably up to 3 nm. The oxidizedlayer exerts its effect as long as its thickness is at least 1 nm.Although the surface oxidized layer may also be formed by increasing theamount of oxygen in the sputtering gas during the sputtering step,atmospheric oxidation or oxidative treatment as mentioned above ispreferred for forming a less defective layer.

In the phase shift mask blank of the invention, a second film of singlelayer or multilayer structure may be formed on the phase shift film.Most often, the second film is disposed contiguous to the phase shiftfilm. Examples of the second film include a light-shielding film, acombination of light-shielding film and antireflective film, and anauxiliary film which functions as a hard mask during subsequent patternformation of the phase shift film. When a third film is formed as willbe described later, the second film may be utilized as an auxiliary film(etching stop film) which functions as an etching stopper duringsubsequent pattern formation of the third film. The second film ispreferably composed of a chromium-containing material.

One exemplary embodiment is a phase shift mask blank illustrated in FIG.2A. The phase shift mask blank depicted at 100 in FIG. 2A includes atransparent substrate 10, a phase shift film 1 formed on the substrate,and a second film 2 formed on the film 1.

The phase shift mask blank may include a light-shielding film as thesecond film on the phase shift film. A combination of a light-shieldingfilm and an antireflective film may also be used as the second film. Theprovision of the second film including a light-shielding film ensuresthat a phase shift mask includes a region capable of completelyshielding exposure light. The light-shielding film and antireflectivefilm may also be utilized as an auxiliary film during etching. Theconstruction and material of the light-shielding film and antireflectivefilm are known from many patent documents, for example, Patent Document4 (JP-A 2007-033469) and Patent Document 5 (JP-A 2007-233179). Onepreferred film construction of the light-shielding film andantireflective film is a structure having a light-shielding film ofCr-containing material and an antireflective film of Cr-containingmaterial for reducing reflection by the light-shielding film. Each ofthe light-shielding film and the antireflective film may be a singlelayer or multilayer. Suitable Cr-containing materials of which thelight-shielding film and antireflective film are made include chromiumalone, chromium oxide (CrO), chromium nitride (CrN), chromium carbide(CrC), chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromiumnitride carbide (CrNC), chromium oxynitride carbide (CrONC) and otherchromium compounds.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the light-shieldingfilm is made of a chromium base material having a chromium content of atleast 40 at %, especially at least 60 at % and less than 100 at %,preferably up to 99 at %, and more preferably up to 90 at %. Thechromium base material has an oxygen content of at least 0 at % and upto 60 at %, preferably up to 40 at %, with an oxygen content of at least1 at % being preferred when an etching rate must be adjusted. Thechromium base material has a nitrogen content of at least 0 at % and upto 50 at %, preferably up to 40 at %, with a nitrogen content of atleast 1 at % being preferred when an etching rate must be adjusted. Thechromium base material has a carbon content of at least 0 at % and up to20 at %, preferably up to 10 at %, with a carbon content of at least 1at % being preferred when an etching rate must be adjusted. The totalcontent of chromium, oxygen, nitrogen and carbon is preferably at least95 at %, more preferably at least 99 at %, and especially 100 at %.

Where the second film is a combination of a light-shielding film and anantireflective film, the antireflective film is preferably made of achromium-containing material having a chromium content of preferably atleast 30 at %, more preferably at least 35 at % and preferably up to 70at %, and more preferably up to 50 at %. The chromium-containingmaterial preferably has an oxygen content of up to 60 at %, and at least1 at % and more preferably at least 20 at %. The chromium-containingmaterial preferably has a nitrogen content of up to 50 at %, morepreferably up to 30 at %, and at least 1 at %, more preferably at least3 at %. The chromium-containing material preferably has a carbon contentof at least 0 at % and up to 20 at %, more preferably up to 5 at %, witha carbon content of at least 1 at % being preferred when an etching ratemust be adjusted. The total content of chromium, oxygen, nitrogen andcarbon is preferably at least 95 at %, more preferably at least 99 at %,and especially 100 at %.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the second film has athickness of typically 20 to 100 nm, preferably 40 to 70 nm. Also thephase shift film combined with the second film should preferably have atotal optical density of at least 2.0, more preferably at least 2.5, andeven more preferably at least 3.0, with respect to exposure light ofwavelength up to 200 nm.

In the phase shift mask blank of the invention, a third film of singlelayer or multilayer structure may be formed on the second film. Mostoften, the third film is disposed contiguous to the second film.Examples of the third film include a light-shielding film, a combinationof light-shielding film and antireflective film, and an auxiliary filmwhich functions as a hard mask during subsequent pattern formation ofthe second film. The third film is preferably composed of asilicon-containing material, especially chromium-free silicon-containingmaterial.

One exemplary embodiment is a phase shift mask blank illustrated in FIG.2B. The phase shift mask blank depicted at 100 in FIG. 2B includes atransparent substrate 10, a phase shift film 1 formed on the substrate,a second film 2 formed on the film 1, and a third film 3 formed on thesecond film 2.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the third film may bean auxiliary film (etching mask film) which functions as a hard maskduring subsequent pattern formation of the second film. When a fourthfilm is formed as will be described later, the third film may beutilized as an auxiliary film (etching stop film) which functions as anetching stopper during subsequent pattern formation of the fourth film.The auxiliary film is preferably composed of a material having differentetching properties from the second film, for example, a material havingresistance to chlorine dry etching applied to the etching ofchromium-containing material, specifically a silicon-containing materialwhich can be etched with fluoride gas such as SF₆ or CF₉. Suitablesilicon-containing materials include silicon alone, a materialcontaining silicon and one or both of nitrogen and oxygen, a materialcontaining silicon and a transition metal, and a material containingsilicon, one or both of nitrogen and oxygen, and a transition metal.Exemplary of the transition metal are molybdenum, tantalum andzirconium.

Where the third film is an auxiliary film, it is preferably composed ofa silicon-containing material having a silicon content of preferably atleast 20 at %, more preferably at least 33 at % and up to 95 at %, morepreferably up to 80 at %. The silicon-containing material has a nitrogencontent of at least 0 at % and up to 50 at %, preferably up to 30 at %,with a nitrogen content of at least 1 at % being preferred when anetching rate must be adjusted. The silicon-containing material has anoxygen content of at least 0 at %, preferably at least 20 at % and up to70 at %, preferably up to 66 at %, with an oxygen content of at least 1at % being preferred when an etching rate must be adjusted. Thesilicon-containing material has a transition metal content of at least 0at % and up to 35 at %, preferably up to 20 at %, with a transitionmetal content of at least 1 at % being preferred if present. The totalcontent of silicon, oxygen, nitrogen and transition metal is preferablyat least 95 at %, more preferably at least 99 at %, and especially 100at %.

Where the second film is a light-shielding film or a combination of alight-shielding film and an antireflective film and the third film is anauxiliary film, the second film has a thickness of typically 20 to 100nm, preferably 40 to 70 nm, and the third film has a thickness oftypically 1 to 30 nm, preferably 2 to 15 nm. Also the phase shift filmcombined with the second film should preferably have a total opticaldensity of at least 2.0, more preferably at least 2.5, and even morepreferably at least 3.0, with respect to exposure light of wavelength upto 200 nm.

Where the second film is an auxiliary film, a light-shielding film maybe formed as the third film. Also, a combination of a light-shieldingfilm and an antireflective film may be formed as the third film. Hereinthe second film may be utilized as an auxiliary film (etching mask film)which functions as a hard mask during pattern formation of the phaseshift film, or an auxiliary film (etching stop film) which functions asan etching stopper during pattern formation of the third film. Examplesof the auxiliary film are films of chromium-containing materials asdescribed in Patent Document 6 (JP-A 2007-241065). The auxiliary filmmay be a single layer or multilayer. Suitable chromium-containingmaterials of which the auxiliary film is made include chromium alone,chromium oxide (CrO), chromium nitride (CrN), chromium carbide (CrC),chromium oxynitride (CrON), chromium oxycarbide (CrOC), chromium nitridecarbide (CrNC), chromium oxynitride carbide (CrONC) and other chromiumcompounds.

Where the second film is an auxiliary film, the film preferably has achromium content of preferably at least 40 at %, more preferably atleast 50 at % and up to 100 at %, more preferably up to 99 at %, andeven more preferably up to 90 at %. The film has an oxygen content of atleast 0 at %, and up to 60 at %, preferably up to 55 at %, with anoxygen content of at least 1 at % being preferred when an etching ratemust be adjusted. The film has a nitrogen content of at least 0 at %,and up to 50 at %, preferably up to 40 at %, with a nitrogen content ofat least 1 at % being preferred when an etching rate must be adjusted.The film has a carbon content of at least 0 at % and up to 20 at %,preferably up to 10 at %, with a carbon content of at least 1 at % beingpreferred when an etching rate must be adjusted. The total content ofchromium, oxygen, nitrogen and carbon is preferably at least 95 at %,more preferably at least 99 at %, and especially 100 at %.

On the other hand, the light-shielding film and antireflective film asthe third film are preferably composed of a material having differentetching properties from the second film, for example, a material havingresistance to chlorine dry etching applied to the etching ofchromium-containing material, specifically a silicon-containing materialwhich can be etched with fluoride gas such as SF₆ or CF_(e) Suitablesilicon-containing materials include silicon alone, a materialcontaining silicon and nitrogen and/or oxygen, a material containingsilicon and a transition metal, and a material containing silicon,nitrogen and/or oxygen, and a transition metal. Exemplary of thetransition metal are molybdenum, tantalum and zirconium.

Where the third film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the light-shieldingfilm and antireflective film are preferably composed of asilicon-containing material having a silicon content of preferably atleast 10 at %, more preferably at least 30 at % and less than 100 at %,more preferably up to 95 at %. The silicon-containing material has anitrogen content of at least 0 at % and up to 50 at %, preferably up to40 at %, especially up to 20 at %, with a nitrogen content of at least 1at % being preferred when an etching rate must be adjusted. Thesilicon-containing material has an oxygen content of at least 0 at %,and up to 60 at %, preferably up to 30 at %, with an oxygen content ofat least 1 at % being preferred when an etching rate must be adjusted.The silicon-containing material has a transition metal content of atleast 0 at % and up to 35 at %, preferably up to 20 at %, with atransition metal content of at least 1 at % being preferred if present.The total content of silicon, oxygen, nitrogen and transition metal ispreferably at least 95 at %, more preferably at least 99 at %, andespecially 100 at %.

Where the second film is an auxiliary film and the third film is alight-shielding film or a combination of a light-shielding film and anantireflective film, the second film has a thickness of typically 1 to20 nm, preferably 2 to 10 nm, and the third film has a thickness oftypically 20 to 100 nm, preferably 30 to 70 nm. Also the phase shiftfilm combined with the second and third films should preferably have atotal optical density of at least 2.0, more preferably at least 2.5, andeven more preferably at least 3.0, with respect to exposure light ofwavelength up to 200 nm.

In the phase shift photomask blank of the invention, a fourth film ofsingle layer or multilayer structure may be formed on the third film.Most often, the fourth film is disposed contiguous to the third film.Exemplary of the fourth film is an auxiliary film which functions as ahard mask during subsequent pattern formation of the third film. Thefourth film is preferably composed of a chromium-containing material.

One exemplary embodiment is a phase shift mask blank illustrated in FIG.2C. The phase shift mask blank depicted at 100 in FIG. 2C includes atransparent substrate 10, a phase shift film 1 formed on the substrate,a second film 2 formed on the film 1, a third film 3 formed on thesecond film 2, and a fourth film 4 formed on the third film 3.

Where the third film is a light-shielding film or a combination of alight-shielding film and an antireflective film, the fourth film may bean auxiliary film (etching mask film) which functions as a hard maskduring subsequent pattern formation of the third film. The auxiliaryfilm is preferably composed of a material having different etchingproperties from the third film, for example, a material havingresistance to fluorine dry etching applied to the etching ofsilicon-containing material, specifically a chromium-containing materialwhich can be etched with oxygen-containing chloride gas. Suitablechromium-containing materials include chromium alone, chromium oxide(CrO), chromium nitride (CrN), chromium carbide (CrC), chromiumoxynitride (CrON), chromium oxycarbide (CrOC), chromium nitride carbide(CrNC), chromium oxynitride carbide (CrONC) and other chromiumcompounds.

Where the fourth film is an auxiliary film, the film has a chromiumcontent of at least 40 at %, preferably at least 50 at % and up to 100at %, preferably up to 99 at %, and more preferably up to 90 at %. Thefilm has an oxygen content of at least 0 at % and up to 60 at %,preferably up to 40 at %, with an oxygen content of at least 1 at %being preferred when an etching rate must be adjusted. The film has anitrogen content of at least 0 at % and up to 50 at %, preferably up toat %, with a nitrogen content of at least 1 at % being preferred when anetching rate must be adjusted. The film has a carbon content of at least0 at % and up to 20 at %, preferably up to 10 at %, with a carboncontent of at least 1 at % being preferred when an etching rate must beadjusted. The total content of chromium, oxygen, nitrogen and carbon ispreferably at least 95 at %, more preferably at least 99 at %, andespecially 100 at %.

Where the second film is an auxiliary film, the third film is alight-shielding film or a combination of a light-shielding film and anantireflective film, and the fourth film is an auxiliary film; thesecond film has a thickness of typically 1 to 20 nm, preferably 2 to 10nm, the third film has a thickness of typically 20 to 100 nm, preferably30 to 70 nm, and the fourth film has a thickness of typically 1 to 30nm, preferably 2 to 20 nm. Also the phase shift film combined with thesecond and third films should preferably have a total optical density ofat least 2.0, more preferably at least 2.5, and even more preferably atleast 3.0, with respect to exposure light of wavelength up to 200 nm.

The second and fourth films of chromium-containing materials may bedeposited by reactive sputtering using a chromium target or a chromiumtarget having one or more of oxygen, nitrogen and carbon added thereto,and a sputtering gas based on a rare gas such as Ar, He or Ne, to whicha reactive gas selected from oxygen-containing gas, nitrogen-containinggas and carbon-containing gas is added depending on the desiredcomposition of a film to be deposited.

The third film of silicon-containing material may be deposited byreactive sputtering using a silicon target, silicon nitride target,target containing silicon and silicon nitride, transition metal target,or composite silicon/transition metal target, and a sputtering gas basedon a rare gas such as Ar, He or Ne, to which a reactive gas selectedfrom oxygen-containing gas, nitrogen-containing gas andcarbon-containing gas is added depending on the desired composition of afilm to be deposited.

The mask blank may be processed into a mask by a standard technique. Forexample, a phase shift mask blank comprising a phase shift film and asecond film of chromium-containing material deposited thereon may beprocessed as follows. First, a resist film adapted for electron beam(EB) lithography is formed on the second film of the phase shift maskblank, exposed to a pattern of EB, and developed in a conventional way,forming a resist pattern. While the resist pattern thus obtained is usedas etching mask, oxygen-containing chlorine base dry etching is carriedout for transferring the resist pattern to the second film, obtaining apattern of the second film. Next, while the second film pattern is usedas etching mask, fluorine base dry etching is carried out fortransferring the pattern to the phase shift film, obtaining a pattern ofthe phase shift film. If any region of the second film is to be left, aresist pattern for protecting that region is formed on the second film.Thereafter, the portion of the second film which is not protected withthe resist pattern is removed by oxygen-containing chlorine base dryetching. The resist pattern is removed in a conventional manner,yielding a phase shift mask.

In another example, a phase shift mask blank comprising a phase shiftfilm, a light-shielding film or a light-shielding film/antireflectivefilm of chromium-containing material deposited thereon as a second film,and an auxiliary film of silicon-containing material deposited thereonas a third film may be processed as follows. First, a resist filmadapted for EB lithography is formed on the third film of the phaseshift mask blank, exposed to a pattern of EB, and developed in aconventional way, forming a resist pattern. While the resist patternthus obtained is used as etching mask, fluorine base dry etching iscarried out for transferring the resist pattern to the third film,obtaining a pattern of the third film. While the third film pattern thusobtained is used as etching mask, oxygen-containing chlorine base dryetching is carried out for transferring the third film pattern to thesecond film, obtaining a pattern of the second film. The resist patternis removed at this point. Further, while the second film pattern is usedas etching mask, fluorine base dry etching is carried out fortransferring the second film pattern to the phase shift film to define apattern of the phase shift film and at the same time, removing the thirdfilm pattern. If any region of the second film is to be left, a resistpattern for protecting that region is formed on the second film.Thereafter, the portion of the second film which is not protected withthe resist pattern is removed by oxygen-containing chlorine base dryetching. The resist pattern is removed in a conventional manner,yielding a phase shift mask.

In a further example, a phase shift mask blank comprising a phase shiftfilm, an auxiliary film of chromium-containing material depositedthereon as a second film, and a light-shielding film or alight-shielding film/antireflective film of silicon-containing materialdeposited on the second film as a third film may be processed asfollows. First, a resist film adapted for EB lithography is formed onthe third film of the phase shift mask blank, exposed to a pattern ofEB, and developed in a conventional way, forming a resist pattern. Whilethe resist pattern thus obtained is used as etching mask, fluorine basedry etching is carried out for transferring the resist pattern to thethird film, obtaining a pattern of the third film. While the third filmpattern thus obtained is used as etching mask, oxygen-containingchlorine base dry etching is carried out for transferring the third filmpattern to the second film, whereby a pattern of the second film isobtained, that is, a portion of the second film where the phase shiftfilm is to be removed is removed. The resist pattern is removed at thispoint. A resist pattern for protecting a portion of the third film to beleft is formed on the third film. Further, while the second film patternis used as etching mask, fluorine base dry etching is carried out fortransferring the second film pattern to the phase shift film to define apattern of the phase shift film and at the same time, removing theportion of the third film which is not protected with the resistpattern. The resist pattern is removed in a conventional manner.Finally, oxygen-containing chlorine base dry etching is carried out toremove the portion of the second film where the third film has beenremoved, yielding a phase shift mask.

In a still further example, a phase shift mask blank comprising a phaseshift film, an auxiliary film of chromium-containing material depositedthereon as a second film, a light-shielding film or a light-shieldingfilm/antireflective film of silicon-containing material deposited on thesecond film as a third film, and an auxiliary film ofchromium-containing material deposited on the third film as a fourthfilm may be processed as follows. First, a resist film adapted for EBlithography is formed on the fourth film of the phase shift mask blank,exposed to a pattern of EB, and developed in a conventional way, forminga resist pattern. While the resist pattern thus obtained is used asetching mask, oxygen-containing chlorine base dry etching is carried outfor transferring the resist pattern to the fourth film, obtaining apattern of the fourth film. While the fourth film pattern thus obtainedis used as etching mask, fluorine base dry etching is carried out fortransferring the fourth film pattern to the third film, obtaining apattern of the third film. The resist pattern is removed at this point.A resist pattern for protecting a portion of the third film to be leftis formed on the fourth film. Further, while the third film pattern isused as etching mask, oxygen-containing chlorine base dry etching iscarried out for transferring the third film pattern to the second film,obtaining a pattern of the second film and at the same time, removingthe portion of the fourth film which is not protected with the resistpattern. Next, while the second film pattern is used as etching mask,fluorine base dry etching is carried out for transferring the secondfilm pattern to the phase shift film to define a pattern of the phaseshift film and at the same time, removing the portion of the third filmwhich is not protected with the resist pattern. The resist pattern isremoved in a conventional manner. Finally, oxygen-containing chlorinebase dry etching is carried out to remove the portion of the second filmwhere the third film has been removed and the portion of the fourth filmwhere the resist pattern has been removed, yielding a phase shift mask.

In a photolithographic method for forming a pattern with a half pitch ofup to 50 nm, typically up to 30 nm, and more typically up to 20 nm on aprocessable substrate, comprising the steps of forming a photoresistfilm on the processable substrate and exposing the photoresist film tolight of wavelength up to 200 nm, typically ArF excimer laser (193 nm)or F₂ laser (157 nm), through a patterned mask for transferring thepattern to the photoresist film, the phase shift mask of the inventionis best suited for use in the exposure step.

The phase shift mask obtained from the mask blank is advantageouslyapplicable to the pattern exposure method comprising projecting light tothe photomask pattern including the pattern of phase shift film fortransferring the photomask pattern to an object (photoresist film) onthe processable substrate. The irradiation of exposure light may beeither dry exposure or immersion exposure. The pattern exposure methodis effective particularly when a wafer of at least 300 mm as theprocessable substrate is exposed to a photomask pattern of light by theimmersion lithography with the tendency that a cumulative irradiationenergy dose increases within a relatively short time in commercial scalemicrofabrication.

EXAMPLE

Examples are given below for further illustrating the invention althoughthe invention is not limited thereto.

Example 1

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. A halftone phase shift film of SiNwas deposited by using a silicon target as the sputtering target andargon and nitrogen gases as the sputtering gas, applying a power of1,900 W across the target, and adjusting the flow rate of argon gas to17 sccm and the flow rate of nitrogen gas to 40 sccm. Before and afterdeposition of the halftone phase shift film, a warpage change (ΔTIR) ina central region of 142 mm squares on the substrate surface was measuredby a flatness tester Tropel® UltraFlat 200 Mask (Corning Inc.). Theabsolute value of ΔTIR was 0.22 μm. Thereafter, the substrate wastransferred to a heat treating furnace where heat treatment was carriedout at 500° C. for 6 hours in an atmosphere containing nitrogen andoxygen gases under substantially atmospheric partial pressures,completing a halftone phase shift mask blank. Before the deposition ofthe halftone phase shift film and after the heat treatment, the warpagechange (ΔTIR) in a central region of 142 mm squares on the substratesurface had an absolute value of 0.10 μm. The halftone phase shift filmafter heat treatment had a phase shift of 177°, a transmittance of 19%,and a thickness of 60 nm. On X-ray photoelectron spectroscopy (XPS), thefilm had a Si:N atomic ratio of 46:53.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.07 μm.

On a phase shift mask blank having a halftone phase shift film of SiNdeposited under the same conditions as above, a second film ofCr-containing material was formed. A resist film for EB lithography wasformed on the second film. The resist film was exposed patternwise by EBlithography and developed in a customary manner to form a resistpattern. With the resist pattern made etching mask, the second film wassubjected to oxygen-containing chlorine base dry etching to transfer theresist pattern to the second film to form a second film pattern. Withthe second film pattern made etching mask, fluorine base dry etching wascarried out to transfer the second film pattern to the phase shift filmto form a phase shift film pattern. Finally the resist pattern and thesecond film were removed in a customary manner, yielding a phase shiftmask. The resulting phase shift mask allowed for correction by acorrecting device using electron beam.

Example 2

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. A halftone phase shift film of SiONwas deposited by using a silicon target as the sputtering target andargon, nitrogen and oxygen gases as the sputtering gas, applying a powerof 1,900 W across the target, and adjusting the flow rate of argon gasto 15 sccm, the flow rate of nitrogen gas to 40 sccm, and the flow rateof oxygen gas to 2 sccm. Thereafter, the substrate was transferred to aheat treating furnace where heat treatment was carried out at 500° C.for 6 hours in an atmosphere containing nitrogen and oxygen gases undersubstantially atmospheric partial pressures, completing a halftone phaseshift mask blank. Before the deposition of the halftone phase shift filmand after the heat treatment, the warpage change (ΔTIR) in a centralregion of 142 mm squares on the substrate surface had an absolute valueof 0.15 μm. The halftone phase shift film after heat treatment had aphase shift of 175°, a transmittance of 24%, and a thickness of 63 nm.On XPS, the film had a Si:N:O atomic ratio of 43:48:8.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.18 μm.

Example 3

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. Sputter deposition was carried out byusing a silicon target as the sputtering target and argon, nitrogen andoxygen gases as the sputtering gas, and applying a power of 1,900 Wacross the target. A layer of SiN was deposited by adjusting the flowrate of argon gas to 15 sccm and the flow rate of nitrogen gas to 40sccm, and a layer of SiON was then deposited by adjusting the flow rateof argon gas to 10 sccm, the flow rate of nitrogen gas to 40 sccm, andthe flow rate of oxygen gas to 10 sccm. There was obtained a halftonephase shift film consisting of the SiN layer and SiON layer. Thereafter,the substrate was transferred to a heat treating furnace where heattreatment was carried out at 500° C. for 6 hours in an atmospherecontaining nitrogen and oxygen gases under substantially atmosphericpartial pressures, completing a halftone phase shift mask blank. Beforethe deposition of the halftone phase shift film and after the heattreatment, the warpage change (ΔTIR) in a central region of 142 mmsquares on the substrate surface had an absolute value of 0.17 μm. Thehalftone phase shift film after heat treatment had a phase shift of177°, a transmittance of 29%, and a thickness of 66 nm. On XPS, the SiNlayer had a Si:N atomic ratio of 45:54 and the SiON layer had a Si:N:Oatomic ratio of 38:20:41.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.19 μm.

Example 4

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. A halftone phase shift film of SiNwas deposited by using a silicon target as the sputtering target andargon and nitrogen gases as the sputtering gas, applying a power of1,900 W across the target, and adjusting the flow rate of argon gas to17 sccm and the flow rate of nitrogen gas to 30 sccm. Before and afterdeposition of the halftone phase shift film, the warpage change (ΔTIR)in a central region of 142 mm squares on the substrate surface had anabsolute value of 0.41 μm. Thereafter, the substrate was transferred toa heat treating furnace where heat treatment was carried out at 500° C.for 6 hours in an atmosphere containing nitrogen and oxygen gases undersubstantially atmospheric partial pressures, completing a halftone phaseshift mask blank. Before the deposition of the halftone phase shift filmand after the heat treatment, the warpage change (ΔTIR) in a centralregion of 142 mm squares on the substrate surface had an absolute valueof 0.06 μm. The halftone phase shift film after heat treatment had aphase shift of 179°, a transmittance of 7%, and a thickness of 61 nm. OnXPS, the film had a Si:N atomic ratio of 47:52.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.08 μm.

Comparative Example 1

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. A halftone phase shift film of SiNwas deposited by using a silicon target as the sputtering target andnitrogen gas as the sputtering gas, applying a power of 1,900 W acrossthe target, and adjusting the flow rate of nitrogen gas to 50 sccm.Thereafter, the substrate was transferred to a heat treating furnacewhere heat treatment was carried out at 500° C. for 6 hours in anatmosphere containing nitrogen and oxygen gases under substantiallyatmospheric partial pressures, completing a halftone phase shift maskblank. Before the deposition of the halftone phase shift film and afterthe heat treatment, the warpage change (ΔTIR) in a central region of 142mm squares on the substrate surface had an absolute value of 0.44 μm.The halftone phase shift film after heat treatment had a phase shift of175°, a transmittance of 18%, and a thickness of 60 nm. On XPS, the filmhad a Si:N atomic ratio of 45:54.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.45 μm.

Comparative Example 2

In a chamber of a sputtering system, a 6025 quartz substrate of 152 mmsquares and 6.35 mm thick was set. A halftone phase shift film of SiNwas deposited by using a silicon target as the sputtering target andargon and nitrogen gases as the sputtering gas, applying a power of1,900 W across the target, and adjusting the flow rate of argon gas to17 sccm and the flow rate of nitrogen gas to 30 sccm. Before and afterdeposition of the halftone phase shift film, the warpage change (ΔTIR)in a central region of 142 mm squares on the substrate surface had anabsolute value of 0.41 μm. Thereafter, the substrate was transferred toa heat treating furnace where heat treatment was carried out at 300° C.for 6 hours in an atmosphere containing nitrogen and oxygen gases undersubstantially atmospheric partial pressures, completing a halftone phaseshift mask blank. Before the deposition of the halftone phase shift filmand after the heat treatment, the warpage change (ΔTIR) in a centralregion of 142 mm squares on the substrate surface had an absolute valueof 0.24 μm. The halftone phase shift film after heat treatment had aphase shift of 179°, a transmittance of 7%, and a thickness of 61 nm. OnXPS, the film had a Si:N atomic ratio of 47:52.

Next, the halftone phase shift film on the quartz substrate of thehalftone phase shift mask blank was completely removed by fluorine basedry etching. Before and after removal of the halftone phase shift film,the warpage change (ΔTIR) in a central region of 142 mm squares on thesubstrate surface had an absolute value of 0.27 μm.

Japanese Patent Application No. 2015-072766 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A phase shift mask blank comprising a transparent substrate of 152 mmsquares and 6.35 mm thick and a phase shift film deposited on thesubstrate and having a phase shift of 150 to 200° with respect to lightof wavelength up to 200 nm, wherein said phase shift film includes atleast one layer composed of a silicon base material consisting ofsilicon, nitrogen and up to 20 at % of oxygen, has a thickness of up to70 nm, and provides a warpage change (ΔTIR) of up to 0.2 μm as absolutevalue in a central region of 142 mm squares on a surface of thesubstrate between before the deposition of the phase shift film on thesubstrate and the presence of the phase shift film on the substrate. 2.A phase shift mask blank comprising a transparent substrate of 152 mmsquares and 6.35 mm thick and a phase shift film deposited on thesubstrate and having a phase shift of 150 to 200° with respect to lightof wavelength up to 200 nm, wherein said phase shift film includes atleast one layer composed of a silicon base material consisting ofsilicon, nitrogen and up to 20 at % of oxygen, has a thickness of up to70 nm, and provides a warpage change (ΔTIR) of up to 0.2 μm as absolutevalue in a central region of 142 mm squares on a surface of thesubstrate between the presence of the phase shift film on the substrateand after complete removal of the phase shift film from the substrate byetching.
 3. The mask blank of claim 1 wherein said phase shift film is ahalftone phase shift film composed of a silicon base material consistingof silicon, nitrogen and oxygen and having a transmittance of at least20% with respect to light of wavelength up to 200 nm.
 4. The mask blankof claim 1, further comprising a second film on the phase shift film,the second film being a single layer or a multilayer film composed of achromium-containing material.
 5. The mask blank of claim 4 wherein thesecond film is a light-shielding film, a combination of light-shieldingfilm and antireflective film, or an auxiliary film which functions as ahard mask during pattern formation of the phase shift film.
 6. The maskblank of claim 4 further comprising a third film on the second film, thethird film being a single layer or a multilayer film composed of asilicon-containing material.
 7. The mask blank of claim 6 wherein thesecond film is a light-shielding film or a combination oflight-shielding film and antireflective film, and the third film is anauxiliary film which functions as a hard mask during pattern formationof the second film.
 8. The mask blank of claim 6 wherein the second filmis an auxiliary film which functions as a hard mask during patternformation of the phase shift film and as an etch stopper during patternformation of the third film, and the third film is a light-shieldingfilm or a combination of light-shielding film and antireflective film.9. The mask blank of claim 6, further comprising a fourth film on thethird film, the fourth film being a single layer or a multilayer filmcomposed of a chromium-containing material.
 10. The mask blank of claim9 wherein the second film is an auxiliary film which functions as a hardmask during pattern formation of the phase shift film and as an etchstopper during pattern formation of the third film, the third film is alight-shielding film or a combination of light-shielding film andantireflective film, and the fourth film is an auxiliary film whichfunctions as a hard mask during pattern formation of the third film. 11.The mask blank of claim 1 wherein the phase shift film has been sputterdeposited and heat treated at 400° C. or above for at least 5 minutes.12. A phase shift mask prepared from the phase shift mask blank ofclaim
 1. 13. A phase shift mask blank comprising a transparent substrateof 152 mm squares and 6.35 mm thick and a phase shift film deposited onthe substrate and having a phase shift of 150 to 200° with respect tolight of wavelength up to 200 nm, wherein said phase shift film includesat least one layer composed of a silicon base material consisting of 40to 55 at % of silicon, nitrogen and oxygen, has a thickness of up to 70nm, and provides a warpage change (ΔTIR) of up to 0.2 μm as absolutevalue in a central region of 142 mm squares on a surface of thesubstrate between before the deposition of the phase shift film on thesubstrate and the presence of the phase shift film on the substrate. 14.A phase shift mask blank comprising a transparent substrate of 152 mmsquares and 6.35 mm thick and a phase shift film deposited on thesubstrate and having a phase shift of 150 to 200° with respect to lightof wavelength up to 200 nm, wherein said phase shift film includes atleast one layer composed of a silicon base material consisting of 40 to55 at % of silicon, nitrogen and oxygen, has a thickness of up to 70 nm,and provides a warpage change (ΔTTR) of up to 0.2 μm as absolute valuein a central region of 142 mm squares on a surface of the substratebetween the presence of the phase shift film on the substrate and aftercomplete removal of the phase shift film from the substrate by etching.15. The mask blank of claim 13 wherein said phase shift film is ahalftone phase shift film composed of a silicon base material consistingof silicon, nitrogen and oxygen and having a transmittance of at least20% with respect to light of wavelength up to 200 nm.
 16. The mask blankof claim 13, further comprising a second film on the phase shift film,the second film being a single layer or a multilayer film composed of achromium-containing material.
 17. The mask blank of claim 16 wherein thesecond film is a light-shielding film, a combination of light-shieldingfilm and antireflective film, or an auxiliary film which functions as ahard mask during pattern formation of the phase shift film.
 18. The maskblank of claim 16 further comprising a third film on the second film,the third film being a single layer or a multilayer film composed of asilicon-containing material.
 19. The mask blank of claim 18 wherein thesecond film is a light-shielding film or a combination oflight-shielding film and antireflective film, and the third film is anauxiliary film which functions as a hard mask during pattern formationof the second film.
 20. The mask blank of claim 18 wherein the secondfilm is an auxiliary film which functions as a hard mask during patternformation of the phase shift film and as an etch stopper during patternformation of the third film, and the third film is a light-shieldingfilm or a combination of light-shielding film and antireflective film.21. The mask blank of claim 18, further comprising a fourth film on thethird film, the fourth film being a single layer or a multilayer filmcomposed of a chromium-containing material.
 22. The mask blank of claim21 wherein the second film is an auxiliary film which functions as ahard mask during pattern formation of the phase shift film and as anetch stopper during pattern formation of the third film, the third filmis a light-shielding film or a combination of light-shielding film andantireflective film, and the fourth film is an auxiliary film whichfunctions as a hard mask during pattern formation of the third film. 23.The mask blank of claim 13 wherein the phase shift film has been sputterdeposited and heat treated at 400° C. or above for at least 5 minutes.24. A phase shift mask prepared from the phase shift mask blank of claim13.
 25. A method for preparing a phase shift mask blank comprising thesteps of: sputter depositing a phase shift film on a transparentsubstrate, said depositing step including a step of depositing a layercomposed of a silicon base material consisting of silicon, nitrogen andoxygen on a transparent substrate by using a sputtering system with achamber and at least one silicon target, and feeding argon gas, and atleast one gas selected from nitrogen gas, oxygen gas and nitrogen oxidegas into the chamber, and heat treating the phase shift film on thesubstrate at 400° C. or above for at least 5 minutes.